A medical device comprising an article of polyurethane elastomer. More specifically, the invention relates to radiation cross-linked thermoplastic polyurethane elastomer articles having xe2x80x9cshape memoryxe2x80x9d for use as protective and/or insulative sheaths of medical devices like biomedical electrical leads.
A biomaterial is a systemic, pharmacologically inert substance designed for placement, implantation or incorporation into the body of an organism. A living body constitutes a site that is chemically and biologically hostile to anything that invades it. Thus, materials to be placed, implanted or incorporated must have properties very similar to those of the animal of interest in order not to trigger an immune response in the body. In addition, the materials must be durable since they will be subjected to a variety of biological stresses including motion, temperature, abrasion and wear.
Traditionally, silicone rubber was used as such a biomaterial, but manufacturers have become aware of the superior mechanical properties of polymeric biomaterials including polyurethane, polypropylene and polyimide. A number of medical devices have been fabricated from thermoplastic polyurethane (TPU) elastomer. TPUs are less thrombogenic than silicone rubber and higher in tensile strength. Therefore, outer sheaths formed from TPUs to protect and/or insulate a medical device from bodily fluids and/or tissues may be thinner than sheaths of silicone rubber. However, attachment of sheaths composed of TPUs to medical devices generally requires the use of an adhesive, or other time-consuming manual processes. Such methods often result in the production of a poor seal between the medical device and its outer sheath. Thus, there is a need for a protective and/or insulative outer sheath for medical devices that forms a tight seal with the device and can be assembled by a simple process, without the use of adhesives or solvents.
A process for preparing medical devices comprising a heat shrinkable (with shape memory) polyurethane sheath is provided. The process involves molding, extruding or casting a polyurethane composition into a shaped article, irradiating the article, expanding the article, placing the article around an underlying assembly and then heating the article such that it shrinks to form an intimate seal.
A medical device comprising a shape memory, heat shrinkable polyurethane article is also provided. The polyurethane article is comprised of one or more thermoplastic urethane polymer and one or more monomer cross-linkers.
A method to encase a medical device assembly in a heat shrinkable, shape memory thermoplastic polyurethane article is provided. The polyurethane functions as a protective and/or insulative sheath and is fabricated by molding, extruding or casting the polyurethane composition into a shaped article. The method to encase a medical devise in the heat shrinkable, shape memory thermoplastic polyurethane comprises irradiating the article, expanding the article, placing the article around a medical device assembly, and heating the article to conform to the medical device assembly, i.e., the article shrinks to form an intimate seal between the medical device and the polyurethane article.
These and other embodiments, aspects, advantages and features of the present invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art by reference to the following description of the invention and referenced drawings or by practice of the invention.